windows 7 How does Windows determine dual-boot?

[News Bot]

I want to understand the mechanics of multiple-booting.  Feel free to point me to Microsoft links which explain this.

 

How does Windows know how many bootable OS are present?  Does Windows query each partition at boot to see if an OS resides there?  Or is a pointer added to the MBR as each OS is installed so Windows merely needs to check the MBR?

 

Let me complicate the qustion slightly.  Suppose multiple disks are involved, each with an OS or two.  If Windows queries each partition at boot to see if an OS resides there, then multiple disks does not change anything.  However, if Windows stores this

information in the MBR, how does that work for multiple disks, each with its own MBR?  Does Windows look at every MBR it can find at boot?

 

One more question.  If Windows adds a pointer for each OS to the MBR, then what happens if an OS is deleted, for example, when a partition is deleted or a disk containing an OS or two is physically removed?

 

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